This is a multicenter perspective, controlled clinical trial, to evaluate the Emergency Department use of Tc-99 m sestamibi scanning to aid in the ED triage of patients presenting with symptoms suggestive of acute cardiac ischemia with normal or non-diagnostic electrocardiogram. The primary aim will be to assess the impact of sestamibi scanning on triage decisions; the degree to which those patients with acute cardiac ischemica are hospitalized and those without ischemia are not hospitalized. The secondary aim will be to assess the impact of the use of sestamibi scanning on actual hospital costs. The study will involve 6 hospitals and approximately 5200 subjects. Following a training period, a 19 month data collection period will begin which consists of alternating months of conventional treatment, no imaging, and acute sestamibi imaging. These periods will consist of alternating months. During the months when imaging is performed, patients will be injected with sestamibi as soon as feasible, following their arrival to the ED. They will only be recruited into the protocol if they have chest pain felt to be consistent with cardiac ischemia and have no diagnostic findings of ischemia or infarction on the electrocardiogram. They will then be transported to nuclear medicine after stabilization for imaging. The results of the images will be communicated to the patient and to the referring physician. Usual evaluation, including demographic, clinical, electrocardiographic and enzymatic evaluation will be initiated in the ED and continued through the hopsitalization or observation. Information will be recorded regarding all of these results on case report forms. Irrespective of whether or not imaging is performed, all patients will have cardiac enzymes obtained, and if discharged, will be asked to return within 24 hours for follow-up and conclusion of the enzymatic evaluation. If follow-up would take place during the weekend, further evaluation will be deferred for 72 hours. Additionally, patients will be contacted by telephone for additional follow-up data 30 days after the initial presentation, and records will be reviewed to allow for accurate follow-up information. The goal of the study is to ascertain the cost effectiveness of myocardial perfusion imaging in patients with non-diagnostic electrocardiograms, suspected of acute myocardial ischemia.